Setting keepalive option before opening session

Add the default Homebrew path for OpenSSL certs on OS X

vars_files haven't been discussed yet

Setting the keepalive option before opening up the paramiko session
in order to avoid the slim chance that the connection is stalled
in the short time between opening the session and setting up the
keepalive. I described the issue I am solving at
https://groups.google.com/forum/#!topic/ansible-project/rkwvz3vyvLk

Also removing cruft code from earlier iteration on task.py and fixing
a bug where 'shell' was not removed from the task ds after munge()
cleaned things up

Also reworking tests to cut down on the number of patches required
by sub-classing the DataLoader() class and reworking the base object's
structure a bit to allow its use

Update playbooks_variables.rst

As per yum module documents it state only support 'present, absent and latest'

Current intro doc is pointing older way of using yum module.

I think this is a chapter ordering thing... vars_files have not actually be explained yet (aside from a mention of them in the note right above, which also might need reconsidering?) I think they do get introduced in the next section 'Variables'.

* added ability to set parents (will be used when the deps are loaded)
* added role caching, so roles are not reloaded needlessly (and for
  use in detecting when roles have already been run)
* reworked the way metadata was stored - now individual attribute fields
  instead of a dictionary blob

Update playbooks_roles.rst

Typo fix in playbooks_intro.rst

Ignore compiled Python for documentation.

Update developing_modules.rst

Fix the synopsis in ansible-pull man page.

Small punctuation/grammar fix.

When running `ansible-doc --list` a lot of errors are
generated when `ansible-doc` tries to find documentation
strings in `.pyc` files.

There is some kind of duplicated content with http://docs.ansible.com/faq.html#how-do-i-loop-over-a-list-of-hosts-in-a-group-inside-of-a-template and this gotcha isn't listed here.

Fixes #9316